Would I be able to classify them as Capital Ships if , when Drinax is big enough to afford it, Oleb decided to sell Artwork, antiques, jewels and jewels for 26,400,000,000 credits and spend around 21,980,670,000 credits on 4 of these 5,000 ton Beauties and 1 10,000 ton version of The 8,000 Ton Ritchey Escort, which will, if their recently revealed plan for part 7 goes right, give Drinax A Royal Guard Fleet of 4 5,000 ton, 1 10,000 ton and 1 8,000 ton ships

Just remember that its not just the cost of building / buying capital ships but maintenance costs and manpower. ( Not to mention you need the correct facilities to build or buy them from.)

Purchasing them, either new or used, shouldn't be a terrible problem. Shipyards are always willing to take credits, and jump-capable ships can travel from a more technologically advanced area under their own power.

But you point out a valid issue that whenever a more advanced ship is purchased and it's meant to be stationed far away from where they need to source spares it's a problem. A supply chain makes the ship vulnerable in space dock as in battle.

Capital Ships also get the notice of the major powers which can lead to blocking sales to lesser powers, also hard to get personnel with experience in operating capital ships out on the fringes.

Not as had as you might think. Smaller planets and navies will send their officers to larger naval academies to get training, and even serve. Same goes for senior non-coms. Ratings would be obtained locally.

It was relatively common in the late 1800s and early 1900s for England to build state of the art warships for smaller powers like Chile, and Brazil. The major powers still sell or transfer older warships to nominal allies and neutrals today. While they may have outlived their usefulness to the major power, they are highly valued by the new owner.

And England helped with naval officer training as well. For Traveller you could have mercs provide some training, though I woudn't want them to provide crew for naval warships.

JMIBEST was referring specifically to Drinax and only looking at the profits of the adventurers.

Most neutral powers have a relationship and are in a specific sphere of influence in order to get hand me down military hardware, capital class assets require more care in order not to upset balances in the spheres of influence.